We broke the plastic ring around the side without the adjuster button. We pulled the seat belt cord up, unclipped it at the yellow connector, and was able to install one seat cover.

Trying not to break the other plastic ring, I am not sure how hard to push the paperclip in the hole, because either I'm not hitting the right spot inside, or not pushing hard enough in the hole, or not pulling hard enough on the head rest - - because I can't get it to slide off.

I don't want to take the seat back off, because I fear that will be even harder to return to original order.